Exemplary embodiments of the invention relate to a device for holding and aligning a useful component, in particular of an optical element or an electrical or chemical thrust nozzle.
Such a device is used in space travel for setting and regulating so-called tip/tilt and focus positions, for example, of thrust nozzles or optical elements. The adjustment is performed, for example, with the aid of stepping motors. The position of a respective stepping motor is determined by additional sensors, which are generally optical sensors. Depending on the number of the required stepping motors, possibly required transmissions, and the suspensions thereof, such a device for holding and aligning can have a significant weight. The control, the scalability, and the possible adaptations for different systems are accordingly complex. Such devices are thus susceptible to faults and require extensive and costly tests before use.
Exemplary embodiments of the present invention are directed to a device for holding and aligning a useful component, which is used in space travel in particular, this device being structurally and/or functionally improved.
According to exemplary embodiments of the present invention a device for holding and aligning a useful component, in particular an optical element or an electrical or chemical thrust nozzle, comprises a first and a second housing part and a tilting device. The first housing part is implemented on a first end for stationary arrangement on a carrier, in particular a space vehicle. The second housing part is implemented on a second end for connecting the useful component. The first end and the second end come to rest, in relation to a longitudinal axis of the device, on opposing sides or ends of the device. The tilting device mechanically connects the first housing part and the second housing part to one another and enables a defined alignment and holding of the relative position of the second housing part in relation to the first housing part. The tilting device comprises, as an actuator, a number of wires made of a shape-memory alloy, wherein the length of each of the number of wires is adjustable individually by a respective determination of the resistance, which can be processed as a control variable in a control loop.
The invention therefore uses the electro-thermal-mechanical behavior of a number of wires made of a shape-memory alloy (SMA) as a motor or actuator. The resistance behavior of the shape-memory alloy is fed back as a control variable in a control loop and is therefore used as an inherent position sensor.
Therefore, the change of the specific resistance of the number of wires during the phase transition from martensite into austenite is used, wherein the resistance is processed as a control variable of the tilting device. The extension or shortening (and therefore its absolute length) of a respective wire and therefore the position of the wire in the lateral direction in space can be determined via the dedicated change of the resistance.
Such a device has a high weight savings in relation to a conventional device having stepping motors, transmissions, and sensors. The device can be scaled and adapted in a simple manner. It may therefore be used for various useful components without extensive and costly verification tests.
In particular, it is possible to dispense with position sensors, since, as described, the inherent properties of a shape-memory alloy are used to determine the position of the individual actuators in space.
In addition, the invention has the following further advantages:
The complexity of the mechatronic system is low due to the omission of many electronic components. The shape-memory alloys enable the greatest possible mechanical energy usage with the least possible structural space. The device has a high level of robustness and reliability for holding and aligning the useful component.
The first and the second housing parts can be implemented as at least sectionally cylindrical. The longitudinal axis of the device can then be considered to be the rotational axis
A defined alignment is to be understood, originating from a plane (x-y plane), which is perpendicular to the longitudinal axis of the device, as a (more or less) arbitrary inclination of the plane in relation to the longitudinal axis (z axis).
According to one embodiment, the number of wires is connected in each case in a mechanically fixed manner to the first and the second housing parts. More precisely, a respective first end of a respective wire is connected to the first housing part and a respective second end is connected to the second housing part. The location of the number of wires between the first and the second parts is thus known, so that a precise position for determination is enabled.
The number of wires can consist of a nickel-titanium alloy. A nickel-titanium alloy (NiTi) is also referred to as Nitinol. Nitinol is the intermetallic phase NiTi with an ordered cubic crystal structure differing from that of titanium and nickel. It consists in large part of nickel and a further large part of titanium. The alloy is corrosion-resistant and high strength, and also pseudo-elastically deformable. The transformation temperature may be influenced via the alloy ratio.
According to a further embodiment, the number of wires is arranged in parallel to the longitudinal axis of the device. Furthermore, it is advantageous if the number of wires is of equal thickness. The change of the length of one or more wires then results in an alignment of the second housing part in relation to the first housing part in dependence on the arrangement between the first and the second housing parts.
It is furthermore advantageous if the tilting device comprises at least one spring element, which attempts to press the first and the second housing part away from one another, and/or a cone-socket connection element, which enables arbitrary pivoting of the second housing part in relation to the first housing part. In conjunction with the at least one spring element, which is embodied in particular as a compression spring, and/or the cone-socket connection element, the alignment and reset of the alignment of the second housing part in relation to the first housing part can occur in a defined manner.
According to a further advantageous embodiment, the first and the second housing parts are connected to one another via a release mechanism, which blocks a relative movement of the first and the second housing parts in a starting configuration and enables a relative movement of the first and the second housing parts in an operating configuration. An alignment of the second housing part in relation to the first housing part is thus enabled in the operating configuration. In the starting configuration, the first and the second housing parts are rigidly connected to one another, which is advantageous during the start of a space vehicle in orbit, for example, and to avoid the introduction of excessive forces into the device, in particular into the tilting device having the wires.
According to a further embodiment, the first and the second housing parts are spaced apart from one another via the tilting device at least in the operating configuration. In this way, the relative movement of the second housing part in relation to the first housing part is enabled. In contrast, the first and the second housing parts can press against one another in the starting configuration. The relative position of first and second housing parts in the starting configuration is determined by the structure of the release mechanism. The contact of the two housing parts ensures, during the start of a space vehicle, that no relative movement of the two housing parts in relation to one another is possible, which could thus possibly damage the number of wires and further components of the tilting device.
In order not to damage the wires before the operation of the device, the number of wires is not tensioned in the starting configuration. In contrast, it is provided that after triggering of the release mechanism, the at least one spring element tensions the number of wires.
The tilting movement of the second housing part in relation to the first housing part can be implemented in various ways. Each of the variants described hereafter has advantages in this case with respect to the precision and the system status requirement, wherein all variants can be used equivalently with regard to the use of a number of wires made of a shape-memory alloy as an actuator while using the resistance behavior as a control variable in a control loop.
In the first variant, the tilting device comprises a spring, which is pre-tensioned between the first and the second housing parts, and which is arranged essentially in the region of the longitudinal axis of the device. The wires are tensioned in parallel along the rotor axis by the spring, which is embodied as a compression spring. Furthermore, after the triggering of the release mechanism, the device can be moved from the starting configuration into the operating configuration by the compression spring.
Furthermore, in this variant the tilting device comprises three wires, which are arranged equidistantly, i.e., in a 120° arrangement, on a circle about the longitudinal axis of the device. It is thus possible to incline the second housing part in relation to the first housing part in an arbitrary manner.
In the second and third variants, the cone-socket connection element is arranged centrally in the region of the longitudinal axis of the device instead of the compression spring.
In the second variant, the tilting device comprises two wires, wherein the two wires are arranged on a circle offset by 90° about the longitudinal axis in relation to one another. A compression spring is associated with each of the wires which, in relation to the longitudinal axis, is arranged on the circle opposite to the associated wire. It is furthermore provided that the spring associated with one wire counteracts the wire on the opposite side in the same lever ratio. This principle acts about both axes, which are defined by the arrangement of the two wires on the circuit about the longitudinal axis and the associated compression springs. That is, one axis is formed by a line on which a first of the wires, the associated compression spring, and the intersection point with the longitudinal axis lie. The other axis is formed by another line, on which the other (second) of the wires, the associated compression spring, and the intersection point with the longitudinal axis lie.
In the third variant, the tilting device comprises four wires, which are distributed equidistantly on a circle about the longitudinal axis of the device. This means the four wires are arranged offset to one another by 90° about the longitudinal axis. Each two wires are connected to one another in the same lever ratio as a lever via the centrally arranged cone-socket connection element as a rocker. These wires operate antagonistically. In this case, the applied tension can be interrupted in any arbitrary position, whereby unpowered operation is possible.